1. Field of the Invention
This invention relates to electronic apparatus and method for the transmission and reception of data, control signals and the like between various components comprising a system. More particularly, the invention relates to apparatus and methods for transmitting data between apparatus comprising a complex system, such as an aircraft simulator, in a manner which is inexpensive, easy to maintain and less susceptible to electromagnetic interference than signal transmission techniques found in the prior art.
2. Description of the Prior Art
There are many and varied electronic systems presently in operation which require the transmission of vast amounts of information from a source (such as a computer) to individual load devices. As an example, the interconnection system of present-day aircraft simulators consists of a multitude of cables, patch panels or cabinets, individually wired back plates, and numerous series disconnects, all serving to tie together a complex consisting of widely separated components such as a computer, cockpit instruments and controls, instructor operation station, and several cabinets of signal conditioning and electronic conversion devices. This type of present-day simulator may well include over 2500 independent transmission channels (both analog and digital, but predominantly analog), some of which are separated by distances greater than 100 feet. Some of the problems, such as the large amount of hardware and the interconnecting wiring associated with such a complex simulation system, are apparent by visual inspection. Two of these readily apparent problems which are significant include:
(a) the requirement of extensive use of interconnection cables and associated patch panels or cabinet assemblies; and PA0 (b) the frequent and necessary use of very long interconnecting cables, which use results in degradation of signal quality due to the noise picked up by the long cables.
For example, if an aircraft simulator complex using 2500 transmission channels, each requiring two wires which, on an average, cover a distance of fifty feet, then there would be on the average of approximately fifty feet during which each of 5000 wires was subject to outside interference or about fifty miles (80 kilometers) of wire subject to outside interference. Further, the transmission of analog signals through standard twisted pairs subjects the signal to outside influences due to distributed impedance, particularly where the signals change at a rapid rate. Thus, the long distances and the complicated wiring patterns involved introduce very unfavorable signal-to-noise conditions which are responsible for significant degradation of simulator performance.
However, what is not so readily apparent as the above-mentioned problems is the complex, time-consuming bookkeeping and signal documentation which is necessary to accomplish the wiring and to facilitate trouble shooting and maintenance. Additional penalties associated with the presently available interconnection systems are found when one considers the impact on manufacturing processes, inventory control, and maintenance tasks. Each of these tasks is based on (in fact, is hampered by) the prior art techniques used for packaging and interconnection. For example, equipment testing at a systems level cannot be accomplished until simulator fabrication is almost complete and the necessary associated signal conditioning hardware and interconnecting cables have been installed.
In addition to the common interconnecting technique of using a single transmission channel for each control signal or bit of data, some efforts have been made in the past to provide better and more efficient systems. One particularly valuable system that does provide significant improvement over the standard technique of signal and data distribution is described in U.S. Pat. No. 3,848,230 issued to John F. Rehm and Evan E. M. Lloyd on Nov. 12, 1974. However, notwithstanding the advantages and savings in the number of conductors disclosed by the Rehm et al patent over the standard technique, there is still a significant amount of low-use hardware and a large number of conductors necessary.
More specifically, past techniques of interfacing the simulator general purpose digital computer with the end item loads and devices included functionalized equipment modules or components at various different locations. Each particular piece of equipment provided a certain type of signal processing or conditioning. Thus, the interconnection of several equipment modules was often necessary to completely process or condition a single signal which originated from one end item so that it would be compatible and suitable for use by the piece of equipment requiring the data or signal to continue operation. That is, the information or data generated by one simulator end item may not be of suitable form, magnitude, polarity, etc., for use by another end item such as, for example, the computer which requires information or data for proper operation. In such a situation, the information cannot simply be transmitted or routed directly from the source end item to the using end item, but must instead first be routed to the necessary equipment to properly condition and process the information so that it can be used by the end item. Typically, the distribution and conditioning task can be categorized and is handled by the prior art equipment as follows:
(a) The linkage equipment converts the simulator general purpose digital computer signals to analog and discrete output signals which are required by the simulator loads. Similarly, this equipment converts analog and discrete signals generated by the various simulator end items to digital signals in the form required by the general purpose digital computer. Most prior art simulator complexes use one piece of centralized linkage equipment for all such conversions performed. However, in systems of the type taught in the aforementioned Rehm et al patent, linkage equipment was divided in several similar but smaller pieces of equipment which were positioned at selected locations throughout the simulator complex to various simulator load or end use devices.
(b) Signal conditioning equipment or hardware provide further processing or conditioning of the signal converted by the linkage equipment to meet the requirements of the end item or using device. Similarly, conditioning of signal outputs from the end item are often required prior to application to the linkage equipment after which the converted signal is transmitted to the simulator general purpose digital computer.
(c) The interconnection between the components, the signal conditioning equipment, the linkage equipment and the end items involved a massive number of cables, connectors and patch panel assemblies. Most of the prior art simulators utilize a centralized interconnecting scheme or interface cabinet where all connections for simulator loads, linkage and signal conditioning hardware were brought to a common location and then interconnected. The system taught by the Rehm et al patent, however, somewhat reduced the length of cable required and the number of interconnections by distributing the interconnecting panels or cabinets about the simulator complex and closer to the various pieces of equipment.
(d) In the prior art simulators, the power distribution system consists of a central group of cabinets containing power supplies. The power from the various power supplies is distributed to and shared by all of the equipment making up the complex. This technique, of course, requires a large distribution network of massive power lines which requires an equal number of massive return lines. The power distribution system taught by Rehm et al reduces the large power network somewhat by providing many separate power supplies at various equipment locations.